A study of observer variability in CT Scan reading and coding was implemented utilizing identical sets of CT Scan polaroids and the CT Scan Data Collection form of the Pilot Traumatic Coma Data Bank. Readers were neurosurgeons participating in the Coma Data Bank (Z01 NS 02340-03 OBFS). The degree of agreement among readers was calculated by Kappa statistics and an item analysis was performed. Severity of errors was determined by a substantive analysis.